This invention relates to a method and system for processing medical image data to aid in the detection and diagnosis of disease, and more particularly, to a method and system for measuring tissue changes associated with chronic lung disease in medical images obtained from an x-ray computed tomography (CT) system.
An x-ray chest radiograph system is the more commonly used diagnostic tool useful for the purpose of detecting lung disease in humans. Lung disease such as bronchitis, emphysema and lung cancer are also detectable in chest radiographs and CT. However, CT systems generally provide over 80 separate images for a single CT scan thereby providing a considerable amount of information to a radiologist for use in interpreting the images and detecting suspect regions that may indicate disease.
Suspect regions are defined as those regions a trained radiologist would recommend following through subsequent diagnostic imaging, biopsy, functional lung testing, or other methods. The considerable volume of data presented by a single CT scan presents a time-consuming process for radiologists. Conventional lung cancer screening generally involves a manual interpretation of the 80 or more images by the radiologist. Fatigue is therefore a significant factor affecting sensitivity and specificity of the human reading. In other diseases, such as emphysema, it is difficult for a radiologist to classify the extent of disease progression by only looking at the CT images.
Chronic Obstructive Pulmonary Disease (COPD) is identified based on symptoms including coughing, wheezing, and shortness of breath (dyspnea). COPD includes a number of respiratory diseases, the most prominent of which are emphysema and chronic bronchitis. COPD affects large airways, small airways and parenchyma in patients. Diseases are typically caused by smoking and air pollution, and are linked to genetic predisposition causing alpha-anti-elastase deficiency.
Emphysema, or airspace destruction, is the most prominent feature of parenchymal change in COPD patients. Emphysema is the result of the loss of elastic recoil of lung tissue. There are four types of emphysema: centrilobular, panlobular or panacinar, distal acinar or paraseptal, and irregular. The first two types contribute to the majority of emphysematous COPD. The classification is based on the anatomical distribution of airspace destruction within a lobule, which is a cluster of acini. Currently, emphysema can be classified only through post mortem examination. Emphysema is typically diagnosed by gross physiological responses, medical imaging and post mortem anatomical inspection. The use of high resolution CT image data is a promising technique for measuring the lung volume for diagnosis purposes. However, one of the more prominent disease indicators is degradation of the alveoli and other tissue changes of the lung which are currently difficult to measure from CT image data.
Detecting emphysema at early stages is most desirable. The damage caused by emphysema is often detected at later stages of the disease and the effects are permanent. Although the effects of emphysema cannot be reversed, early diagnosis of emphysema may enable measures to be taken by the patient to prevent further progression of the damage caused by the disease. Further, as more and more therapy and drug treatments are discovered, it will be desirable to monitor a patient's response to such treatment.
What is needed is a robust method and system for measuring disease relevant tissue changes in medical images to enable diagnosis and tracking of various forms of COPD.